The present invention relates to an oxide superconductor and a method of manufacturing the same.
To allow an oxide superconductor to transport a large current, the oxide superconductor is required to be highly oriented to exhibit an electromagnetic anisotropy and to be less in grain boundary acting as a weak link. To meet these requirements, it was customary in the past to form an oxide superconductor film by vapor phase growth on an oriented oxide and/or metal substrate.
However, the deposition rate of the oxide superconductor film is considerably low in the vapor phase growing method, leading to a long time required for forming a film thick enough to transport a large current. In addition, the vapor phase growing method is known to bring about poor orientation and increased grain boundaries with increase in the thickness of the oxide superconductor film (Jpn. J. Appl. Phys. Vol. 31 (1992) pp.2709-2715 and Supercond. Sci. Technol. 8 (1993) pp.23-29, Printed in the UK). The vapor phase growing method is also known to give rise to cracks in the formed superconductor film, leading to breakage of the current path, with increase in the thickness of the film.
A measure for solving the above-noted problems is proposed in, for example, Japanese Patent Disclosure (Kokai) No. 6-321694. Specifically, it is proposed to form an oxide superconductor film on a substrate by liquid phase epitaxy. This method certainly permits forming a relatively thick oxide superconductor film, which is less in grain boundary, in a short time. However, it is impossible to eliminate completely the cracks occurring in the oxide superconductor film, leaving room for further improvement in the critical current density of the oxide superconductor film.